Metering of liquid coolant in open-circuit liquid-cooled gas turbines

ABSTRACT

Weir construction precisely located relative to the shaft axis of a liquid-cooled gas turbine is employed to meter coolant flow to the cooling channels in turbine buckets.

United States Patent Kydd METERING OF LIQUID COOLANT IN OPEN-CIRCUITLIQUID-COOLED GAS UNITED STATES PATENTS TURBINES- 3,446,482 5/ I969 Kydd..416 /90 [72] Inventor: Paul H. Kydd, Scotia, NY. 2,991,973 7/196! Coleet al ..4l6/97 [73] Assign: General Electric Campany PrimaryExaminer-Everette A. Powell, Jr. 7 [22] Filed: Nov. 27, 1970 AssistantExaminer-Clemens Schimikowski Attorney-Richard R. Brainard, Paul A.Frank, Charles T. [2]] Appl' 934,56 Watts, Leo l. Malossi, Frank L.Neuhauser, Oscar B. Waddell and Joseph B, Forman [52] [1.5. CI ..416/97,416/92, 416/95 [51] Int. Cl ..F0ld 5/18 [57] ABSTRACT [58] Field ofSearch 51 11 Weir construction precisely located relative to the shaftaxis of a liquid-cooled gas turbine is employed to meter coolant flow tothe cooling channels in turbine buckets.

4 Claims, 4 Drawing Figures a a i l /3 I w, /5 l 4 26 Z6 a Lu, 1

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PATENTEDAPR 25 I972 SHEET 2 BF 2 Paul MK 12') van 602- ydci is AttorneyMETERING F LIQUID COOLANT IN OPEN-CIRCUIT LIQUID-COOLED GAS TURBINESBACKGROUND OF THE INVENTION Structural arrangements for the liquidcooling of gas turbine buckets are shown in U.S. Pat. Nos. 3,446,481Kydd. These patents are incorporated by reference.

The provisions for open-circuit liquid cooling disclosed therein areparticularly important for the capability offered thereby for increasingthe turbine inlet temperature to an operating range of from 2,500 F. toat least 3,500 F. thereby obtaining an increase in power output rangingfrom aboutlOO to 200 percent and in an increase in thermal efficiencyranging to as high as 50 percent. Such open-circuit liquid-cooledturbine structures are referred to as ultra high temperature gasturbines.

In such turbines the heat flux to the turbine buckets is so high that itis necessary to have a great many coolant channels in each bucket todistribute the coolant uniformly over the bucket surface. Typically, fora small turbine, the channels will measure about 0.02 X 0.025 inch andbe spaced from about 0.052 to 0.071 inch on center over differentsurface areas of the bucket for a total of about 50 coolant channels perbucket. In a complete turbine rotor there may be as many as 100presenting a total of about 5,000 channels each of which must receive anaccurately metered amount of liquid coolant. Also, in ultra hightemperature gas turbines it is desirable to employ extremely high buckettip speeds (e.g. l ,5 00-2,000 feet/second) in order to remove largeamounts of energy per turbine stage. These high speeds furthercomplicate the problem of coolant metering. Since the centrifugal fieldmay be as much as 250,000 G under such conditions a difference in waterlevel of as little as 0.001 inch is equivalent to a 20 foot head at l G.Thus, even minor inaccuracies in that portion of a metering system (e.g.locations of metering holes or weirs) served by a single source ofcoolant will result in large imbalances in flow in that particularportion due to differences in pressure head.

SUMMARY OF THE INVENTION Weir construction forming part of each platformelement of the turbine rotor is precisely located relative to the shaftaxis of the liquid-cooled gas turbine providing essentially constantflow conditions at all points along all weirs.

BRIEF DESCRIPTION OF THE DRAWING The exact nature of this invention aswell as objects and advantages thereof will be readily apparent fromconsideration of the following specification relating to the annexeddrawings in which:

FIG. 1 is a three-dimensional view partially in cut-away sectiondisplaying the relationship of the weir construction as part ofindividual platform elements relative to the lower ends of the coolantchannels of the adjacent turbine bucket;

FIG. 2 shows the unified bucket/rotor disk rim construction incombination with improved bucket tip construction for the open-circuitsystem for cooling this structure and shows portions of the casingrelated to the bucket tip construction;

FIG. 3 is a section taken on line 3-3 of FIG. 2 and FIG. 4 is an offsetsection taken on line 4-4 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turbine bucket consists of asheet metal skin 11 affixed (e.g. by brazing) to investment cast hollowcore 12 having inwith and terminate at a similar manifold (not shown)recessed into core 12. Near the trailing edge of bucket 10 a cross-overconduit (not shown) connects the manifold on the suction side withmanifold 14.

Requisite open-circuit cooling from manifold 14 (and the manifold on thesuction side) is ensured by the presence of opening 16, which providesfor the exit of the heated cooling fluids from manifold 14 at thetrailing edge of bucket 10 as shown. Annular collection slot 17 formedin casing 18 receives the centrifugally directed ejected fluid for theeventual recirculation or disposed thereof.

The turbine bucket manifolding and collection system is described ingreater detail and is claimed in U.S. Patent application Ser. No. 93,057(Docket RD-3206) Kydd (incorporated by reference) filed Nov. 27, 1970,now pending, and assigned to the assigned of the instant invention.

The root end of core 11 consists of a number of finger-like projections,or tines, 19 of varying length. These projections 19 may present agenerally rectangular profile as shown or each tine may be taperedtoward the distal end thereof to present a generally triangular profile.Rim 21 of turbine disk 22 has grooves 23 machined therein extending tovarious depths and having widths matching the different lengths andwidths of bucket tines 19 such that tines 19 will fit snuggly into thecompleted grooves 23 in an interlocking relationship. Triangularlyshaped bucket tine profiles provide for improved stress distribution inthe joints between tines I9 and grooves 23 in shear and in the tines intension. However, the rectangular profiles are preferred for ease ofmanufacture.

Once the proper fit has been obtained, the appropriate amount of brazingalloy is placed in each groove 23 and the buckets are inserted and heldin fixed position by a fixture. The fixture is biased to maintain atight fit between tines I9 and grooves 23 regardless of thermalexpansion. Conventional brazing alloys having melting points rangingfrom 700 to l,lO0 C. may be used. Single metals, such as copper, mayalso be used.

This interlocking bucket/rotor disk construction is more completelydescribed and claimed in US. Patent application Ser. No, 93,058 (DocketRD-3207) Kydd (incorporated by reference), filled Nov. 27, 1970, nowpending and assigned to the assignee of the instant invention.

Thereafter, the assembly (the rim with all the buckets properly located)is furnace-brazed to provide an integral structure.

Steel alloys may be used for the skin and core, preferably thosecontaining at least 12 percent'by weight of chromium for corrosionresistance and heat treatable to achieve high strength.

The cutting of grooves 23 into rim 2] not only provides the requisiteconfiguration for fastening the bucket root and lessens the weight ofthe rim, but in addition the ribs 24 between grooves 23 provide area onthe upper surfaces thereof for attachment thereto of investment castplatform elements 26 having cooling channels 27 and 28 formed therein.Platform elements 26 may also be prepared by other methods, such as, bycoining. The cooling channels 27 are in juxtaposition with grooves 23and cooling channels 28 interconnect the cooling channels 27 as shown.The separating walls 29 between cooling channels 27 are dimensioned tocoincide with the width of juxtaposed ribs 24.

The improved structure for metering of the liquid coolant is providedduring the preparation of platform elements 26 by accurately grindingeach edge rib 31 to the radius of the outer diameter of the ribs 24thereby providing a cylindrical surface (the elements of which extend inthe axial direction) following bucket 10 on each side thereof adjacentthe cooling channels 13. As will be explained hereinbelow all portionsof those cylindrical surfaces receiving coolant from a commondistribution path must be accurately located equidistant from the axisof rotation. In operation these edge ribs 31 will function a weirs overwhich the cooling fluid can distribute uniformly into the bucket coolingchannels 13 of each bucket uniform sheet. Ribs 24 are each provided withrelief cuts 24a to ensure a clear supply path for the coolant along thelength of ribs 31 to grooves 13a leading to channels 13.

Platform elements 26 are affixed to the rotor rim by the electron beamwelding of separating walls 29 to ribs 24 after previously grinding thedistal face of each wall 29 to a radius common to the outer diameter ofribs 24.

Although the platform construction shown herein consists of individualplatform elements prepared separate from buckets 10 and from each other,other constructions are equally feasible. For example, the platformcomponents may be made integral with each bucket or a single continuousplatform having holes cut therein to accommodate buckets 10 may be used.In each case the weir surfaces distributing coolant to buckets 10 willbe formed as part of the platform construction located adjacent eachside of each bucket 10.

Since the leading edge of buckets 10 is exposed to the highest heatflux, it is more directly (not via weir 31) supplied with liquidcoolant. The manner in which this liquid coolant is supplied is morecompletely described hereihbelow.

As is described in the aforementioned Kydd patents, cooling liquid(usually water) is sprayed at low pressure in a generally radiallyoutward direction from nozzles (now shown, but preferably located oneach side of disk 22) and impinges on disk 22. The coolant thereuponmoves into gutters 32, 32a defined in part by downwardly extending lipportions 33, 33a. The cooling liquid accumulates in gutters 32, 32a(cooling the rim portions with which it comes into contact) beingretained therein until this liquid has accelerated to the prevailingdisk rim velocity.

After the cooling liquid in gutters 32, 32a has been so accelerated,this liquid continually drains from gutters 32, 32a passing radiallyoutward through holes 34, 34a of which holes 34 are in flowcommunication with the two outside grooves 23 (FIGS. 2 and 4) in theregions between buckets 10. As is shown in FIG. 4 specific holes 34acommunicate directly with the cooling channel located at the leadingedge of each of the buckets 10. Thus, some of the liquid coolantby-passes weirs 31 to be provided directly to the leading edges ofbuckets 10 while the remainder of the coolant is introduced into theoutside grooves 23 from which it is distributed via cooling channels 28to the cooling channels 27. As the coolant traverses all these surfacesof the platform elements 26, these elements are kept cool. Thereafter,the coolant passes over the distal faces of edge ribs 31 in thin sheetsinto the radially inner end of cooling channels 13 (via grooves 13a) inadjacent buckets l and thence into and through the turbine buckets.

lt is critical that the portions of gutters 32, 32a draining into holes34, 34a be machined to very close tolerances to ensure equidistancethereof from the center of rotation whereby coolant distribution toholes 34, 34a will be substantially equal. As may be seen in FIG. 4 aset of six holes 34 provides the coolant for the coolant channels in thesuction side of one bucket and in the adjacent pressure side of the nextbucket. Thus, the pair of edge ribs 31 receiving coolant from such acommon source of holes 34 (regardless of whether they are formed in thesame platform element as shown herein, or not) must present weirsurfaces all points along which are equidistant from the center ofrotation to ensure equal distribution of coolant.

As the cooling liquid moves through cooling channels 13 of any givenbucket a large portion) or substantially all of the cooling fluid,depending upon the rate of flow) is converted to the gaseous or vaporstate as it absorbs heat from the skin ll and core 12 of the bucket. Atthe outer ends of cooling chan nels 13 the vapor or gas and anyremaining liquid coolant pass into manifold 14 and the manifold on thesuction face. Thereafter, the flow from the suction manifold is mergedwith the flow in manifold 14 and the combined flows exit therefrom viaopening 16 into collection slot 17 to complete the opencircuit coolingpath.

In the construction illustrated and described the weirs (accuratelylocated cylindrical surfaces), one of which is located in the given liuid coolant distribution Kath leadin to each side of each tur me bucket15 ground to t e radius 0 the outer diameter of ribs 24. However, aradius different from the.

radius of the outer diameter of ribs 24 may be employed, if desired, solong as all portions of those cylindrical surfaces receiving coolantfrom a common upstream distribution path are located equidistant fromthe axis of rotation.

If weirs are used, which extend straight across the underside of theplatform construction, each cooling channel must extend to a locationadjacent the straight weir, so that the liquid coolant traversing theaccurated ground cylindrical surface of the weir (located in accordancewith this invention) will be fed directly to the coolant channels orextensions thereof.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a gas turbine wherein a turbine disk is mounted on a shaftrotatably supported in a casing, said turbine disk extendingsubstantially perpendicular to the axis of said shaft and having turbinebuckets and platform means affixed to the outer rim thereof, saidbuckets receiving a driving force from a hot motive fluid moving in adirection generally parallel to said axis of said shaft and the drivingforce being transmitted to said shaft via said turbine disk, meanslocated radially inward of said platform adjacent said turbine disk forintroducing liquid coolant within said turbine in a radially outwarddirection into open-circuit distribution paths by which said coolanttraverses surface area of said rim and said platform means, passes intocooling channels in said buckets and exits from said channels in aradially outward direction, the improvement comprising:

a. a plurality of separate cylindrical surfaces, the elements of whichextend parallel to the axis of the shaft, each of said surfaces beingformed on the radially inward side of the platform means, one of saidcylindrical surfaces being located in the given liquid coolantdistribution path leading to each side of each turbine bucket adjacentthe inward end of the cooling channels therefor and all portions ofthose cylindrical surfaces receiving coolant from a common downstreamdistribution path being located equidistant from said axis.

2. The improvement of claim 1 wherein a pair of exposed cylindricalsurfaces are formed on a single platform element disposed between a pairof turbine buckets.

3. The improvement of claim 2 wherein the cylindrical surfaces followthe turbine bucket root air-foil configuration.

4. The improvement of claim 1 wherein the platform means has a pluralityof grooves in the underside thereof to facilitate the distribution ofliquid coolant.

I UNITED STATES PATENT OFFICE CERTIFICATE OF (IQ-ERECTION v 3,658,439Dated April 25, 1972 Patent No.

Inventor(s) Paul H. Kydd v It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected" as shown below:

In column 1, the sentence in lines 5 and 6 should read:

- Structural arrangements for the liquid cooling of gas turbine bucketsare shown in U. S. Patent Nos.

3,446,481- Kydd and 3,446,482 Kydda Signed and sealed this 29th day ofAugust 1972'.

(SEAL) Attesti ROBERT GO-TTSCHALK EDWARD M.FLETCHER,JR. V

Commissioner of Patents Attesting Officer 1'' FORM 30-1050 (1069)USCOMM-DC 60376-P69 U.5. GOVERNMENY PHINYING OFFICE: I959 0-35631l

1. In a gas turbine wherein a turbine disk is mounted on a shaftrotatably supported in a casing, said turbine disk extendingsubstantially perpendicular to the axis of said shaft and having turbinebuckets and platform means affixed to the outer rim thereof, saidbuckets receiving a driving force from a hot motive fluid moving in adirection generally parallel to said axis of said shaft and the drivingforce being transmitted to said shaft via said turbine disk, meanslocated radially inward of said platform adjacent said turbine disk forintroducing liquid coolant within said turbine in a radially outwarddirection into open-circuit distribution paths by which said coolanttraverses surface area of said rim and said platform means, passes intocooling channels in said buckets and exits from said channels in aradially outward direction, the improvement comprising: a. a pluralityof separate cylindrical surfaces, the elements of which extend parallelto the axis of the shaft, each of said surfaces being formed on theradially inward side of the platform means, one of said cylindricalsurfaces being located in the given liquid coolant distribution pathleading to each side of each turbine bucket adjacent the inward end ofthe cooling channels therefor and all portions of those cylindricalsurfaces receiving coolant from a common downstream distribution pathbeing located equidistant from said axis.
 2. The improvement of claim 1wherein a pair of exposed cylindrical surfaces are formed on a singleplatform element disposed between a pair of turbine buckets.
 3. Theimprovement of claim 2 wherein the cylindrical surfaces follow theturbine bucket root air-foil configuration.
 4. The improvement of claim1 wherein the platform means has a plurality of groovEs in the undersidethereof to facilitate the distribution of liquid coolant.